(B) Direct-Current Utilization Circuits. The voltage of

dc utilization circuits shall conform with 210.6. (C) Photovoltaic Source and Output Circuits. Over 600 V not allowed (D) Circuits Over 150 Volts to Ground. NOT accessible to other than qualified persons

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Voltage Rules Summary

PV system voltage (VNEC) is the Voc x 1.25.

wSystems over 600 volts cannot be installed in 1 & 2 family dwellings.

wSystems over 250 volts must use 600 volt equipment and conductors.wSystems over 150 volts, installed in 1 & 2 family dwellings, must be locked.wSystems over 50 volts must be grounded.wSystems less then 50 volts must use 12 AWG conductors (or larger).

NEC Over-current Device Current Rating (Iod)

Iod > 125% X INEC Example: 125% X 10 Amps = 12.5 Amps > 13 Amps (Iod)

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PV Conductor Ampacity So we know that the current could be as high as 10 A under certain irradiance conditions and the over current device is sized with another factor of 1.25 because the PV current is continuous. So now we must have a wire that can carry AT LEAST the amount of current it is protected for (13 A).

Now we have to consider the temperature conditions.

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New temperature calculations in NEC 2008

Table 310.15(B) 2(c)

But whatambient temp doyou use?

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Use theCopperDevelopmentAssociation’s“Outdoordesigntemperatures”

October 2012 PV Installer's Course ---NEC Article 690 Highlights

33Now you take the design temp + temp adder from NEC table 310.15(B)(2)(c)

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1) Must have polarity (labeled + and -)

2) Must have protected tips

3) Must latch together so they can’t be disconnected

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Voltage drop from PV array to inverter

In addition to sizing the wires for ampacity,

we also have to consider voltage drop.

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About Voltage Drop Wires should be sized to reduce resistive (heating) loss to less than 2%. This loss is a function of the SQUARE of the current x the resistance. This is another manifestation of Ohm’s law: V= I x R. So I = V/R. And resistive loss is I x I x R = V/R x V/R x R = V x V/R = our old friend, V x I = Watts!

So “resistive loss” equals power loss, a bad thing.

Use a wire-sizing table to choose the size wire for the

current and voltage you are working with.

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Computing voltage drop formula (0.2 x d x I /V) x (Ω/kf) = %Voltage Drop Where: • I is the circuit current, which for source circuits is usually taken as the maximum power current, Imp, • d = one way distance in feet •V is the voltage at which you want to find VD, and • Ω/kft is the wire’s resistivity in Ohms per 1000 feet and is found from NEC Chapter 9, Table 8, Conductor Properties. • Math note: 2d is the round trip distance. To convert to %, one multiplies by 100, but to convert feet to kilo-feet, one divides by 1000. 2 x 100/1000 = 0.2October 2012 PV Installer's Course ---NEC Article 690 Highlights 48 Grounding See also, article 250

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Grounding: the big picture + -

1) 11) + 4) -

1)

+ - + - 3)

1) 5) 9)

3) 2) 200 A + 8) + 3) + load

- 3) 7) G line 3) line

L1 6) load L2 G 30 A N G

bond wire from new ground rod to existing ground rod or water pipe 3)

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[250.4] Bonding and grounding requirements for non-current carrying conductive components: ★Must be connected together (bonded) ★Must be permanent and continuous ★Must be connected to earth (grounded) ¬Must be connected to the electrical source ¬ Must be in accordance with manufactures instructions. [110.3(B)]

From article 250: don’t forget that the equipment ground

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690.45 Size of Equipment Grounding Conductors.

Equipment grounding conductors for photovoltaic source and photovoltaic outputcircuits shall be sized in accordance with 690.45(A) or (B).(A) General. Equipment grounding conductors in photovoltaic source andphotovoltaic output circuits shall be sized in accordance with Table 250.122. Whereno overcurrent protective device is used in the circuit, an assumed overcurrent devicerated at the photovoltaic rated short-circuit current shall be used in Table 250.122.Increases in equipment grounding conductor size to address voltage dropconsiderations shall not be required. The equipment grounding conductors shall beno smaller than 14 AWG.

(B) Ground-Fault Protection Not Provided. For other than dwelling units where ground-fault protection is not provided in accordance with 690.5(A) through (C), each equipmentgrounding conductor shall have an ampacity of at least two (2) times the temperature andconduit fill corrected circuit conductor ampacity. October 2012 PV Installer's Course ---NEC Article 690 Highlights 53EQUIPMENT GROUNDS

October 2012 PV Installer's Course ---NEC Article 690 Highlights 54

EQUIPMENT GROUNDS

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EQUIPMENT GROUNDS

Wiley Electronics www.we-llc.comILSCO Lug

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EQUIPMENT GROUNDS

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SYSTEM GROUNDS

[250.166] The Grounding

Electrode Conductor to be no smaller then the largest conductor but not smaller the #8 AWG for DC systems.

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SYSTEM GROUNDS

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VI. Marking

Signs, signs, everywhere there’s signs

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Some markings are already there such as on modules. Others, you have to put on, such as:

690.53 Photovoltaic Power Source. A marking, specifying

the photovoltaic power source rated as follows, shall be provided by the installer at the site at an accessible location at the disconnecting means for the photovoltaic power source: (1) Operating current (2) Operating voltage (3) Maximum system voltage (4) Short-circuit current

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690.54 Interactive System Point of Interconnection. Label the breaker PV is tied in to

690.55 Photovoltaic Power Systems Employing Energy

Storage. State Max voltage

690.56 Identification of Power Sources.

Indicate where the disconnects are. 690.64 (B)(4) and (5). Label the breaker which is back-fed by PV system and that it IS back-fed.

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8) Existing service panel

Reminder: Neutral and grounds

for circuits must be separated in all sub-panels.

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VIII. Storage Batteries Highlights: •High-voltage (over 50 V) not allowed unless terminals are inaccessible •Guard live parts. •Make sure there is a fuse or breaker in the + wire of the battery bank. •There has to be disconnect switch •Wet cells must have sufficient ventilation. See Article 480. •Check Article 110.26 for working space rules. Don’t put the power panel directly above the battery bank. •Use battery cables of the correct type.

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Related codes

If batteries are being installed where there is propane, check the

local propane code. Usually, you cannot install a battery bankwithin 3’ of a propane fired appliance.

If the battery box vent goes thru the wall, install a power vent.

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Daily NEC for PVThere are some things that come up in every installation.Other items are taken care of for you. Already figured: •Module interconnect size •GFP fuse comes with inverter •Series string fuse specified on module •AC breaker size specified in inverter instructionsYou have to do:•Size wires and conduits for wiring from PV array to inverter. Consider ampacity, temperatures and voltage drop.•Size wires from inverter to load center.•Put the ground wiring on correctly